46 CHELONIA. 



Emtda vittata. 



Emyda ^dttata, Peters, Monatsher. Berl. Acad. 1854, p. 216. 



This species has been characterized by the black streaks and spots on the head and neck, 

 and is said to have been brought from Goa. 



TRIONYX, Geoffr. 



Shell much depressed, only partly ossified, covered with soft skin, dilated 

 into a broad cartilaginous margin posteriorly. Sternum more or less carti- 

 laginous, sometimes with two pairs of externally visible osseous plates, and 

 with the hinder lobe not dilated into lateral valves. Feet broadly webbed, 

 with three strong claws anteriorly and posteriorly. Muzzle produced into 

 a nasal tube ; snout conically pointed. 



This genus is so closely allied to Emyda in its structure and in its habits, that we may 

 refer to the general description given above. The different species also are extremely similar 

 to one another. Trionyx, however, wants that series of bones which is found in the posterior 

 dilated margin of the upper shell of Emyda ; and instead of seven externally visible ossifica- 

 tions in the sternum, it has only four, viz. the inguinal and the anal pair. The hinder sternal 

 lobe is small, without lateral valves. The head is more elongate than in Emyda, and the 

 tail, although short, always distinct ; it is longer in males than in females. 



The species of this genus are found in North America, Africa, and the East Indies ; they 

 are the largest of the Freshwater Turtles, and thoroughly aquatic and carnivorous. 



Various methods of distinguishing the difierent species must be resorted to : one character 

 is the colours, more distinct during life and in young indi\dduals, but changing with age ; 

 another character is the arrangement of small tubercles on the skin of the upper shell, 

 visible only in (young) specimens, fresh or preserved in spirits; finally, a third and very 

 important character is the structure and shape of the ossified plates, which can be examined 

 only in dried, more or less full-grown individuals. 



Trionyx sinensis. 



Trionyx sinensis, Wiegm. N&v. Act. Acad. Leop. Carol, xvii. 1835, p. 189. Strauch, Chelonolog. 

 Stud. p. 177. 



tuberculatus, Cantor, Ann. &; Mag. Nat. Hist. ix. 1842, p. 482. 



Tyrse perocellata, G?-ay, Catal. Tort. Brit. Mus. p. 48. 

 Trionyx perocellatus, Gray, Catal. Shield Kept. p. 65. tab. 31. 



Shell of the adult. — The bony carapace rather longer than broad, with a low but very 

 distinct vertebral ridge. The anterior dorsal bone short, broad, rugose like the other costal 



